(CNN) -- Somali militants vowed to rescue a Saudi supertanker that was hijacked by pirates a week ago, according to residents of a town where the pirates are believed to be based.

Five armored vehicles loaded with al-Shabab fighters arrived in the central Somali coastal town of Harardhere this weekend, near where pirates are holding the massive oil tanker Sirius Star, said Ahmed Mohamed, a resident of the town.

The fighters told residents they would battle the pirates because the tanker, which is loaded with 2 million barrels of oil, is owned by a Muslim country and should not have been taken, Mohamed said.

Another resident, Hassan Nor, suggested that the al-Shabab fighters' motive was to share in the multimillion-dollar ransom the pirates have demanded from the supertanker's owner.

The al-Shabab militia is an offshoot of an Islamic party that ruled much of Somalia in the second half of 2006 and aims to impose Islamic sharia law in Somalia. It was forced from power by Ethiopian troops but continues to fight for control.

Nor said he could see the Sirius Star anchored offshore from his town.

"The armed pirates have climbed on the top of the ship," Nor said. "They vowed that they will defend any attackers from the ship."

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The owners of the Sirius Star, carrying a cargo valued at $100 million when it was hijacked off the coast of Kenya, are currently involved in negotiations.

"We do not like to negotiate with either terrorists or hijackers, but the owners of the tanker are the owners of the tanker, and they are the final arbiters of what happens there," said Prince Saud Al-Faisal.

More than $150 million has been paid to pirates around the Horn of Africa over the past 12 months, Kenya's foreign minister said Friday.

The money is encouraging them to continue and become more brazen in their attacks, Foreign Minister Moses Wetangula told a news conference in the Kenyan capital.